The invention relates to a braking device for a motor vehicle, comprising a first brake circuit, controlled by the driver of the vehicle, and a second brake circuit controlled by a programmed computer.
The first brake circuit includes a master cylinder controlled in general by a brake pedal, via a pneumatic brake booster, and the second brake circuit includes at least one pump driven by an electric motor and supplied with brake fluid from the master cylinder. The outlet pipes of the master cylinder and of the aforementioned pump are connected to wheel brakes via circuits that include solenoid valves controlled by the computer.
In normal operation, the solenoid valves that connect the outlets of the master cylinder to the wheel brakes are opened by the computer and the wheel brakes are supplied with pressurized brake fluid by the master cylinder of the first brake circuit under the control of the driver when he presses on the brake pedal. During this normal operation, it may happen that a braking command is generated by the computer, which receives setpoint signals from, for example, a software program of the ESP (Electronic Stability Program) or ACC (Active Cruise Control) type.
In this case, the solenoid valves that connect the first brake circuit to the wheel brakes are closed. Because the pressure in the second brake circuit is high, any action by the driver on the brake pedal will result in a very small displacement, one which is very unusual for this pedal and which runs a risk of disturbing and worrying the driver.